940 IAC - is it supposed to be wide open, or shut, with no power?

SmittySmithsonite · Post by **SmittySmithsonite** » 13 Aug 2019, 07:52

New member here. My expertise is on domestic vehicles. Trying to diagnose a bad IAC on this 940 with no service info - frustrating as hell!

Vehicle - '95 Volvo 940 wagon 2.3L 4-cylinder, Bosch system.

All my testing has narrowed it down to the IAC. What I want to know is, as the unit is sitting in my hand, should I be seeing right inside the unit through the port that's pointing down in the first pic? From what I've been reading, this should be closed off with no power applied. Also, this unit has 2 pins - not 3 - for the electrical connection. When I energize the unit, the shutter flips around briefly, and can barely be seen through the port. I can blow air through it regardless of having 12v at the pins, or 0v at the pins.

Thing looks fairly new, and is extremely clean inside as you can see. I sprayed some silicone spray in there to lube and clean things up a bit (not that it needed it - just in case it may have been sticking). Anyone ever looked inside one of these, or better yet, anyone have a known good one laying around to look at? I suspect I should be seeing the shutter closing off that port when there's no voltage applied to the pins. I just need 100% confirmation of this.

Any and all info will be greatly appreciated!

Post by **jimmy57** » 13 Aug 2019, 13:47

It should have a rest position for that valve that should give 900-1200 RPM idle.

SmittySmithsonite · Post by **SmittySmithsonite** » 23 Aug 2019, 14:00

Thanks Jimmy - you're the only one who answered my question out of 3 forums.

I finally have the answer here in my hand. Hopefully this will help someone else down the line who's attempting to keep these 940's on the road.

I hate winging parts at something without thorough troubleshooting, and being 200% sure that a new part will fix the problem. Without service info, I took a chance, based on my limited testing and observation of the old part, and purchased a brand new Bosch idle air control valve. Lo and behold, the shutter is 90% CLOSED on the new one! There's just a tiny opening to the left - 90% of the opening is blocked by the shutter. Exactly what I suspected. Made the right call, and for that I'm happy.

Here's pictures of the new unit taken in the exact location of the old unit in the post above (down the tube with the arrow on it).

: New Bosch idle air control unit

: Shutter 90% closed!

: Slight opening (to left inside tube) to allow default idle air

93Regina · Post by **93Regina** » 29 Aug 2019, 05:22

SmittySmithsonite wrote: ↑23 Aug 2019, 14:00I finally have the answer here in my hand.

Are you sure?

With a choke cable, hooked a water valve, one could rig up a manual IAC....homework is required, but it should work

Post by **E Showell** » 30 Nov 2019, 16:40

What was the effect on drivability with the bad IAC?

93Regina · Post by **93Regina** » 30 Nov 2019, 19:29

E Showell wrote: ↑30 Nov 2019, 16:40effect on drivability with the bad IAC?

IAC - Idle Air Control

IAC is related to idling RPM....irrelevant for roadway drivability...throttle plate is in control.

A bad IAC would have to be defined....stuck is what position...allows extra air, higher RPM...allows smaller amounts, lower RPM (stall out possible).

IIRC, IAC gets a "frequency" based signal (aka duty cycle) when throttle switch is in idle position. Once off idle switch position, your foot is in control

Post by **E Showell** » 30 Nov 2019, 19:35

Reason I ask, daughter's H.S. buddy has a '92 940. I am told it can't be driven over about 40 mph. Not exactly sure what the issue is. I'll try to get more data and report back.

93Regina · Post by **93Regina** » 01 Dec 2019, 08:01

E Showell wrote: ↑30 Nov 2019, 19:35can't be driven over about 40 mph.

LH 2.4 has a limp home mode....Rex-I/Regina I've never heard of a limp home mode.

Bypassing FPR, or low rail pressure (fuel pump or filter defective) would be suspect....by 1993, there was a quick test for checking rail pressure at rail.

Post by **E Showell** » 01 Dec 2019, 08:17

Overdrive relay bad?

93Regina · Post by **93Regina** » 01 Dec 2019, 10:22

E Showell wrote: ↑01 Dec 2019, 08:17Overdrive relay bad?

940s could have had AW70s, or AW71Ls transmissions.

Kickdown cable may not be working correctly....so upper range gears are absent. If so, engine most likely is using higher RPMs

OD relay circuit would only affect shifting into OD...higher speeds than 40mph exist....when OD is kicked out, this is for heavy loads or mountain like driving. Hence, 65 mph....

Kickdown cables fail...they all get replaced....hence, if a gear shifting issue, kickdown cable needs replacement, or valve-body has an issue.